As is well known in the art, in a pulse combustion apparatus air and fuel gas are initially forced into a mixing chamber where the air and the gas are mixed. The mixture is supplied into a combustion chamber where the mixture is ignited in a forced manner, or by an igniting means. Once combustion starts normally in the combustion chamber, the apparatus is "self-sustaining". To be more exact, once combustion starts normally therein, it is no longer necessary to force air and fuel gas into the mixing chamber in order to continue combustion. Instead the combustion chamber draws, by itself, subsequent air and fuel gas through the mixing chamber thanks to the negative pressure which is created, within the combustion chamber, by the initial combustion products produced therein and flowing into a tail pipe. Nor is it necessary to ignite the subsequent air/fuel mixture by the igniting means, but the subsequent mixture ignites itself. This "self-ignition" comes from the possibility that a portion of the initial burned gas which has flowed into the tail pipe may return into the combustion chamber or from the possibility that a portion of the initial burned gas may remain in the combustion chamber. Such a portion of the initial burned gas ignites the subsequent mixture. Thus, in the apparatus, a series of air/fuel mixture supply, ignition, expansion and exhaust occurs in, for example, some 80 to 100 cycles per second. A check-valve mechanism for passing air into the mixing chamber and a check-valve mechanism for passing fuel gas thereinto each are opened and closed in the same cycles as the foregoing series of air/fuel mixture supply, ignition, expansion and exhaust occurs. Thus the check-valve mechanisms are opened and closed at very high rates.
In the conventional pulse combustion apparatus for heating liquid, the check-valve mechanism for passing air into the mixing chamber comprises (i) a circular partition wall separating an air inlet chamber and the mixing chamber from each other, (ii) a plurality of front discs, or valve members, and (iii) a plurality of rear discs. The rear discs are located inside the mixing chamber, and are axially spaced apart from the partition wall by approximately 1.5 to 1.8 millimeters. Each rear disc has a much smaller diameter than the partition wall. The rear discs are arranged with equal intervals, and form, as a whole, a ring which is smaller in diameter than the partition wall, but is concentric with the partition wall. The number of the valve members is the same as that of the rear discs. The valve members are located between the partition wall and the rear discs. Each valve member has a little smaller diameter than the rear disc. The valve members are coaxial with the respective rear discs, and overlie the respective rear discs as viewed from the inlet side of the mixing chamber. Each rear disc has a plurality of small circular openings through which air may pass. Also, the partition wall has a plurality of small circular openings in the portions thereof which correspond to, or coincide with, the respective rear discs. Thus the mixing chamber communicates with the air inlet chamber through the circular openings of the partition wall. Air to be mixed with fuel gas flows into the air inlet chamber, and passes through the openings of the partition wall into the mixing chamber. Each valve member, the associated perforated portion of the partition wall and the associated rear disc have central large openings, and are joined together by means of a common bolt which passes through the central large openings thereof. Each valve member, the associated perforated portion of the partition wall and the associated rear disc, as a whole, constitute a valve section. Each valve member is axially movable between the partition wall and the associated rear disc.
On the other hand, the check-valve mechanism for passing fuel gas into the mixing chamber, or more particularly into a gas distributing chamber, comprises (i) a circular outlet-side wall of a gas inlet chamber, (ii) a single front disc, or valve member, and (iii) a single rear disc. The rear disc is spaced apart from the outlet-side wall of the gas inlet chamber by substantially the same distance as each rear disc of the foregoing check-valve mechanism for air is spaced apart from the partition wall thereof. The rear disc is located outside the gas inlet chamber, and is on a downstream side of the gas inlet chamber. The valve member is located between the outlet-side wall of the gas inlet chamber and the rear disc. The valve member has a little smaller diameter than the rear disc. The rear disc, the valve member and the outlet-side wall of the gas inlet chamber each have a central large opening, and are joined together by means of a common bolt which passes through the central openings thereof. The outlet-side wall of the gas inlet chamber has a plurality of small circular openings. Fuel gas enters the gas inlet chamber, and comes therefrom through these small circular openings. The rear disc also has a plurality of small circular openings through which the gas may pass. The valve member is axially movable between the outlet-side wall of the gas inlet chamber and the rear disc. Thus, the construction of the check-valve mechanism for fuel gas is the same as the construction of each valve section of the check-valve mechanism for air.
Initially air and fuel gas are forced into the mixing chamber. Air blown from a blower enters the air inlet chamber, passes through the circular openings of the partition wall separating the air inlet chamber and the mixing chamber from each other, and enters the mixing chamber. Fuel gas supplied separately from the air enters a gas chamber, and flows into the gas inlet chamber. The gas passes through the circular openings of the outlet-side wall of the gas inlet chamber, and flows into the gas distributing chamber. From the gas distributing chamber the gas is supplied into the mixing chamber. The air and the gas are thus mixed in the mixing chamber. The mixture flows through a flame trap into the combustion chamber. The initial mixture thus supplied into the combustion chamber is ignited in a forced manner, or by an ignition plug. As mentioned before, when the initial mixture is normally ignited to start combustion normally in the combustion chamber, the combustion chamber draws, by itself, subsequent air and fuel gas through the mixing chamber thanks to the negative pressure which is created, within the combustion chamber, by the initial combustion products produced therein and flowing into a tail pipe. Also as mentioned before, the subsequent mixture drawn into the combustion chamber ignites itself.
As mentioned before, such a series of air/fuel mixture supply, ignition, expansion and exhaust occurs in, for example, some 80 to 100 cycles per second. The check-valve mechanisms for passing air into the mixing chamber and for passing fuel gas thereinto each are opened and closed in the same cycles as the series of air/fuel mixture supply, ignition, expansion and exhaust occurs.
Thus the check-valve mechanisms are opened and closed at very high rates per second. When the mixture has been ignited, the combustion chamber has therein a pressure which is considerably higher than the atmospheric pressure. This positive pressure causes the valve members of the check-valve mechanism for air to move to the upstream side and strike the foregoing partition wall. Thus the small circular openings of the perforated portions of the partition wall associated with the respective valve members are closed by the respective valve members, and therefore the entire check-valve mechanism for air is closed. Simultaneously with the closing of this check-valve mechanism, the valve member of the check-valve mechanism for fuel gas also moves to the upstream side and strikes the outlet-side wall of the gas inlet chamber, due to the foregoing positive pressure. Thus the small circular openings of this outlet-side wall are closed by the valve member, and therefore the check-valve mechanism for fuel gas is also closed. After the combustion has taken place in the combustion chamber, the combustion products produced in the combustion chamber flows into the tail pipe, thus reducing the pressure in the combustion chamber below the atmospheric pressure. Then, thanks to the negative pressure thus created in the combustion chamber, subsequent air and fuel are drawn, and causes the valve members of the check-valve mechanism for air and of the check-valve mechanism for fuel gas, respectively, to move away from the associated walls to the downstream sides. Thus the circular openings of the foregoing partition wall and the circular opening of the foregoing outlet-side wall are opened, and therefore the two check-valve mechanisms are opened. The subsequent air and fuel gas are thus supplied.
Thus it may be said that each valve member vibrates axially between the associated wall and the associated rear disc at very high rates per second.
As mentioned above, when the valve members of the checkvalve mechanisms have moved to the upstream sides, the valve members strike the respective associated walls. And when the valve members have struck these walls, the portions of each valve member which closes the circular openings of the associated wall project, or are sucked, into the circular openings to certain degrees. Thus, the portions of each valve member which strike the edges of the circular openings of the associated wall are damaged to certain degrees each time the valve member strikes the associated wall. Therefore, the valve members are damaged out of use sooner or later.
The valve members also strike the respective associated rear discs when the valve members have moved away from the associated walls to the downstream sides. When striking the rear discs, however, the valve members are hardly damaged. The reason for this is that the difference between the atmospheric pressure and the negative pressure in the combustion chamber when the latter pressure has been produced in the combustion chamber is very much smaller than the difference between the positive pressure in the combustion chamber and the atmospheric pressure when the former pressure has been produced in the combustion chamber.
If openings with much smaller sizes than in the prior art may be made, as passages for fluid, through the foremost member of the check-valve mechanism, the service life of the valve member can be prolonged considerably. However, as long as circular openings are made, the sizes thereof cannot be made much smaller since the smaller the openings, the smaller the amount of fluid passing therethrough becomes. Researches conducted by the inventors have shown that if the sizes, or diameters, of the circular openings are reduced below 2 or 3 millimeters, a sufficient rate of flow of fluid cannot be ensured therethrough.
Also, the pulse combustion apparatus may be subjected to high temperatures of more than 300.degree. C. The conventional valve member comprises a sheet metal or a woven fabric of glass fiber coated with resin. However, the valve member of such materials can provide only a very short service life under the severe thermal conditions.